Ampicillin

Ampicillin Full Name

Ampicillin

Ampicillin Introduction

Ampicillin is a classic semi-synthetic broad-spectrum penicillin belonging to the β-lactam class of antibiotics. As one of the earliest developed broad-spectrum penicillins, it significantly expanded the antibacterial spectrum of penicillin, making it effective not only against traditional Gram-positive bacteria but also against certain Gram-negative bacteria, such as Haemophilus influenzae, Escherichia coli, and Salmonella. The core function of ampicillin lies in its potent bactericidal action. Its mechanism of action is similar to that of other β-lactam antibiotics: inhibiting bacterial cell wall biosynthesis. Specifically, ampicillin irreversibly binds to penicillin-binding proteins (PBPs) located on the bacterial cytoplasmic membrane. These proteins are key enzymes that catalyze the final stage of peptidoglycan synthesis, a critical structural component of the cell wall. Once PBPs are inhibited, bacteria cannot form a complete and structurally sound cell wall. This leads to swelling and rupture of the cell under osmotic pressure, ultimately resulting in cell death.

Figure 1. Chemical structures of sultamicillin, ampicillin and sulbactam. (Source: Betrosian AP, et al. 2009)

Based on this mechanism, ampicillin has been widely used to treat a variety of infectious diseases caused by susceptible strains. Its clinical indications are extensive, covering multiple systems including the respiratory, urinary, and digestive tracts. Common therapeutic uses include community-acquired pneumonia, acute otitis media, sinusitis, urinary tract infections, and gastrointestinal infections (such as salmonellosis). Furthermore, ampicillin plays an indispensable role in treating more severe infections, including bacterial meningitis (often used in combination with aminoglycosides, especially in neonates), infective endocarditis, sepsis, and skin and soft tissue infections. Although ampicillin has saved countless lives over the past decades, the most formidable challenge associated with it is the persistent development and spread of bacterial resistance. This is one of the most significant threats to global public health today, severely undermining the clinical efficacy of ampicillin and other antibiotics.

The primary and most common mechanism by which bacteria develop resistance to ampicillin is the production of β-lactamase enzymes. These enzymes specifically hydrolyze the β-lactam ring in the ampicillin molecule, rendering it incapable of binding to PBPs and thereby inactivating the drug. In addition to this enzymatic mechanism, bacteria can acquire resistance through other means. For example, they can alter the structure of their penicillin-binding proteins, reducing the drug's affinity for its target. Alternatively, in the case of Gram-negative bacteria, they can modify the number or structure of porin channels in their outer membrane, restricting the drug's entry into the cell. The emergence and spread of these resistance mechanisms have led to a significant increase in resistance rates to ampicillin among many previously susceptible strains, such as certain E. coli, H. influenzae, and Enterococcus faecalis.

Alternate Names for Ampicillin

Ampicillin

• 1. Diricks M, et al. Revisiting mutational resistance to ampicillin and cefotaxime in Haemophilus influenzae. Genome Med. 2024 Dec 4;16(1):140.
  2. Betrosian AP, et al. Ampicillin-sulbactam: an update on the use of parenteral and oral forms in bacterial infections. Expert Opin Drug Metab Toxicol. 2009 Sep;5(9):1099-112.